Vaccum die casting method and a die for vaccum die casting

ABSTRACT

A vacuum die casting method may include: coupling a fixed die and a movable die to each other; closing a molten metal pouring hole formed in a sleeve using an injection plunger operated in the sleeve, which is formed on a lower side of the fixed die or the movable die; performing vacuum decompression in a cavity formed between the fixed die and the movable die using a vacuum decompression device connected to chill vent blocks provided on upper portions of the fixed die and the movable die; supplying oxygen in the cavity using an oxygen supply device connected to the chill vent blocks after completing the step of performing vacuum decompression; and supplying a molten metal to the cavity through the molten metal pouring hole.

CROSS-REFERENCE(S) TO RELATED APPLICATIONS

This application claims priority to Korean Patent Application No. 10-2019-0140352, filed on Nov. 5, 2019, which is incorporated herein by reference in its entirety.

BACKGROUND OF THE DISCLOSURE Field of the Disclosure

The present disclosure relates to a die casting method and a die, and more particularly, relates to a die casting method and a die, in which the die is cast by creating a vacuum in cavity of the die.

Description of the Related Art

In general, a high pressure casting (die casting) may be performed in a manner whereby a molten metal, which is a melted lightweight non-ferrous metal alloy including aluminum, magnesium and zinc, is injected into a pouring hole of a pouring sleeve. The molten metal is filled into a cavity of a die by an injection plunger at high speed and high pressure, so that a die may be injection molded.

In this process, gases filled in the cavity such as air and steam may be mixed together and remain in the molten metal filled and compressed in the cavity at high speed. In particular, in a case of a product having a complicated shape, it may be more difficult to discharge air, steam and residual gas in the cavity. The air, steam and residual gas in the cavity, which are mixed in the molten metal, may cause a casting defect (blowhole, shrinkage defect, etc.) during cooling and solidification of the molten metal in the die, which lowers strength of the product.

High vacuum die casting uses a technique to dramatically reduce a bubble of the product manufactured by such a die casting method. According to this technique, the product may be manufactured in a following manner. The die is sealed and the air in a die cavity is lowered to 50 mbar or lower using a vacuum pump to allow the die cavity to be in a vacuum state. Then the molten metal is injected into the cavity. Therefore, there is no pore in the product and the product may thus have improved strength when heat treated.

It is impossible to heat treat a common die-casting component having a casting defect in the die. However, the high vacuum die-casting product has no casting defect in the die and may thus have increased mechanical property by about 40% through heat treatment.

However, the high vacuum equipment is very expensive, and the manufacturing cost is increased.

The foregoing is intended merely to aid in understanding the background of the present disclosure, and is not intended to mean that the present disclosure falls within the purview of the related art that is already known to those having ordinary skill in the art.

SUMMARY OF THE DISCLOSURE

The present disclosure has been made in an effort to provide a vacuum die casting method and a die for a vacuum die casting in which a component of high quality and high strength may be manufactured by removing air from a cavity of the die while using no expensive equipment.

In accordance with one aspect of the present disclosure, a vacuum die casting method may include: coupling a fixed die and a movable die to each other; closing a molten metal pouring hole formed in a sleeve using an injection plunger operated in the sleeve, which is formed on a lower side of the fixed die or the movable die; performing vacuum decompression in a cavity formed between the fixed die and the movable die using a vacuum decompression device connected to chill vent blocks provided on upper portions of the fixed die and the movable die; supplying oxygen in the cavity using an oxygen supply device connected to the chill vent blocks after completing the performing of the vacuum decompression; and supplying a molten metal to the cavity through the molten metal pouring hole.

In addition, the vacuum decompression device may be connected to the chill vent blocks through a vacuum decompression line. The oxygen supply device may be connected to the chill vent blocks through the vacuum decompression line and an oxygen supply line.

In addition, in the step of performing vacuum decompression, a vacuum decompression valve provided on the vacuum decompression line may be controlled to be opened following a signal indicating the molten metal pouring hole is closed.

In the step of performing vacuum decompression, the vacuum decompression may be performed until a pressure in the cavity reaches 200 mmHg or less.

Further, the step of supplying oxygen in the cavity may include performing a primary oxygen supply until the pressure in the cavity reaches 1200 mbar or more. The step of supplying the molten metal to the cavity may be performed after the primary oxygen supply is completed. The step of supplying oxygen in the cavity may further include performing a secondary oxygen supply to supply less oxygen than the primary oxygen supply after the step of supplying the molten metal to the cavity is started.

The molten metal may be molten aluminum.

In addition, the vacuum die casting method may further include undertaking an injection step by operating the injection plunger after the step of supplying the molten metal to the cavity. The secondary oxygen supply may be completed at a time point when the injection plunger passes the molten metal pouring hole in the injection step.

In accordance with another aspect of the present disclosure, a die for a vacuum die casting may include: a fixed die and a movable die; an injection plunger operated in a sleeve, which is formed on a lower side of the fixed die or the movable die; a vacuum decompression device connected to chill vent blocks provided on upper portions of the fixed die and the movable die and performing vacuum decompression in a cavity formed between the fixed die and the movable die; and an oxygen supply device connected to the chill vent blocks and performing oxygen supply in the cavity.

In addition, the die for a vacuum die casting may further include: a vacuum decompression line connected from the vacuum decompression device to the chill vent blocks; a vacuum decompression valve provided on the vacuum decompression line; an oxygen supply line connected from the oxygen supply device to the chill vent blocks; and an oxygen supply valve provided on the oxygen supply line.

The vacuum decompression valve may be controlled following a signal of a vacuum sensor provided in the cavity. The oxygen supply valve may be controlled following a signal of an oxygen sensor provided in the cavity.

The chill vent blocks may be formed as a pair in the fixed die and the movable die, respectively. The chill vent blocks may have a molten metal inlet communicating with an upper end of the cavity and introducing the molten metal when the fixed die and the movable die are coupled to each other. The chill vent blocks may have a molten metal solidification flow path extended from the molten metal inlet and a gas discharge hole communicating with the vacuum decompression line.

In addition, the molten metal solidification flow path may have a gap of 1.0 to 1.2 mm.

In addition, a cross section of the molten metal solidification flow path may have triangular uneven structures in an alternating manner such that convex portions and concave portions are repeated and bent several times.

Further, the interior angle of each of the convex portions and the concave portions may have an angle of 40 degrees or less.

The chill vent blocks may have a conformal cooling channel in which a coolant is allowed to efficiently flow.

In accordance with an embodiment of the present disclosure, the device may be simple using relatively low-cost active oxygen and vacuum assist. However, this device may be cast at a cost of about 10% to 20% that of high vacuum equipment and may provide a substantial cost reduction.

This simple device may remove air from the cavity of the die and manufacture a component of high quality and high strength.

This device may exhibit about 30% or more of strength improvement compared to other general die casting devices.

Accordingly, the device in the present disclosure may suppress casting defects caused by residual gas, thereby further extending an application field of die casting having excellent productivity. In particular, this device may allow die casting to be used to manufacture a high-performance component following a trend of motorization and eco-friendliness of automobiles.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the present disclosure should be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a flowchart illustrating a vacuum die casting method according to the present disclosure;

FIGS. 2A, 2B, 2C, 2D, 2E, 2F and 2G sequentially illustrate a vacuum die casting method according to the present disclosure;

FIGS. 3A and 3B illustrate chill vent blocks, which are portions of a die for a vacuum die casting according to the present disclosure;

FIG. 4 illustrates a portion of FIG. 3A; and

FIGS. 5A and 5B comparatively illustrate side surface shapes of molten metal solidified flow paths of the chill vent blocks of FIGS. 3A and 3B.

DESCRIPTION OF EMBODIMENTS

In order to sufficiently understand the present disclosure, operational advantages of the present disclosure and objects accomplished by embodiments of the present disclosure, reference should be made to the accompanying drawings illustrating embodiments of the present disclosure and contents described in the accompanying drawings.

In describing embodiments of the present disclosure, detailed and repetitive descriptions for the known art related to the disclosure have been shortened or omitted where it may otherwise obscure the gist of the disclosure.

FIG. 1 is a flowchart illustrating a vacuum die casting method according to the present disclosure. FIGS. 2A, 2B, 2C, 2D, 2E, 2F and 2G sequentially illustrate a vacuum die casting method according to the present disclosure.

Hereinafter, a vacuum die casting method and a die for a vacuum die casting according to an embodiment of the present disclosure are described with reference to the flowchart of FIG. 1 and to the sequential process of FIGS. 2A-2G.

The present disclosure relates to a method of manufacturing a component of an automobile or the like using a die casting and a die for implementing the method. According to this technique of the present disclosure, a vacuum may be created without a separate expensive vacuum pump forming the vacuum in the die. A corresponding cast product does not have a bubble defect and may thus be heat treated. As a result, a cast component having good strength may be manufactured with a relatively simple configuration and at low cost.

The die for a vacuum die casting may include a fixed die 110 and a movable die 120. First, as illustrated in FIG. 2A, a release-agent spray 130 may be injected onto a surface of a die cavity and the dies may then be closed. In this manner, a casting operation may be prepared (S11).

Chill vent blocks 160 and 160-1 may be provided on upper portions of the fixed die 110 and the movable die 120, which respectively correspond to an upper portion of the cavity. Gases in the die may thereby be discharged within a short time through the chill vent blocks 160 and 160-1 and a molten metal may be prevented from being leaked.

Further, a sleeve 140, which forms or defines a path of the molten metal, may be formed on a lower side of the fixed die 110. An injection path of the molten metal is thereby formed from the sleeve 140 to the cavity.

A molten metal pouring hole 141 into which the molten metal is injected may be formed in the sleeve 140 and coupled to an injection plunger so that the injection plunger is operated along a longitudinal direction of the sleeve 140.

When the fixed die 110 and the movable die 120 are coupled to each other by S11, as illustrated in FIG. 2B, an injection plunger tip 150 may move forward to close the molten metal pouring hole 141 (S12).

A vacuum decompression device 210 and an oxygen supply device 310 may be provided outside of the die to form a vacuum in the cavity. A vacuum decompression line 220 and an oxygen supply line 320, each connected from the vacuum decompression device 210 and the oxygen supply device 310, may be connected to the chill vent blocks 160 and 160-1.

As illustrated in the drawing, the oxygen supply line 320 may be connected to the chill vent blocks 160 and 160-1 by being connected to the vacuum decompression line 220.

Following a signal indicating the molten metal pouring hole 141 is closed (S12), a vacuum decompression valve 230, which is provided on the vacuum decompression line 220, may be controlled to be opened (S21), so that vacuum decompression may be performed in the cavity (S22).

The vacuum decompression may be performed until meeting a preset decompression condition and time (S23). Thereafter, as illustrated in FIG. 2C, the vacuum decompression valve may be controlled to be closed (S24). A decompression condition at S23 may be set to, for example, 200 mmHg or less.

A vacuum sensor may be provided in the cavity to check the condition at S23. S24 may be controlled by a signal of the vacuum sensor.

When the vacuum decompression valve is closed (S24), an oxygen supply valve 330, which is provided in the oxygen supply line 320, may be controlled to be opened (S25), so that oxygen may be supplied into the cavity through the chill vent blocks 160 and 160-1.

Oxygen supply may be performed until meeting the preset compression condition and time (S26). Thereafter, as illustrated in FIG. 2D, the injection plunger tip 150 may move backward (S13) to open the molten metal pouring hole 141. A molten metal m may be quantitatively supplied to the cavity through the opened molten metal pouring hole 141 (S14). When the molten metal supply is completed, as illustrated in FIG. 2E, an injection may proceed (S15).

An oxygen sensor may be provided in the cavity to check the condition at S26. S13 may be controlled by a signal of the oxygen sensor.

Filling or supplying of oxygen may be performed to have a maximum filling capacity for a short time. The filling of oxygen, i.e., oxygen supply, may be performed within, for example, 3 seconds, and under a set pressure set to, for example, 1200 mbar or more.

Even after the supply of molten metal is started, the oxygen supply may not be immediately stopped but may be continuously supplied (S27). However, from a time point when the molten metal pouring hole 141 is opened, an amount of the oxygen supply may be reduced than that at S25.

In the present disclosure, the air in the cavity and sleeve may be replaced with active oxygen through a primary oxygen supply at S25. Chemical reaction between the active oxygen and the molten metal may occur by the molten metal supply and the injection followed by the maximum primary oxygen supply.

The molten metal may, for example, be molten aluminum. When the chemical reaction between the molten metal with active oxygen occurs, fine oxides (Al₂O₃) may be formed to create a local instantaneous vacuum in the cavity. Residual oxygen and reaction products that failed to react with the molten metal may be removed through the injection.

Therefore, in order to create the local instantaneous vacuum in the cavity, the oxygen supply needs to be made also at the molten metal supply S14 before the injection as illustrated in FIG. 2D. The secondary oxygen supply S27 may be 15 to 40% compared to the primary oxygen supply at S25.

In addition, when filling the die cavity with oxygen, i.e., supplying oxygen to the die cavity, it may not be guaranteed that every shot is supplied with oxygen of intact quality even though the oxygen supply is controlled to have a set supply time and an adjusted supply amount. The reason is that the filling of the die cavity with oxygen may depend on a sealing condition of various parting lines of the cavity. To solve this problem, the present disclosure uses a digital pressure gauge as an oxygen sensor to check that the cavity is stably filled with oxygen.

Next, when the injection is started at S15 and the injection plunger tip 150 thus closes the molten metal pouring hole 141 (S16) as illustrated in FIG. 2E, the oxygen supply valve 330 may be controlled to be closed following a signal indicating that the pouring hole is closed. Thus, the oxygen supply may be blocked (S28).

In addition, when the injection plunger tip 150 is switched at high speed (S17), the vacuum decompression valve 230 may be opened to discharge residual gas in the die cavity (S29).

Thereafter, the molten metal is solidified and cooled. Then the dies may be opened as illustrated in FIG. 2G to take out a cast product P.

In the present disclosure, assuming a case where the oxygen is supplied through the sleeve 140 to create the vacuum, a runner portion may be filled with oxygen passing through the sleeve. Then the cavity may be filled with oxygen passing through a gate having a narrow cross-sectional area. Therefore, the die cavity, i.e. an actual portion to be filled with oxygen, may be finally filled with oxygen after oxygen passes through such a gate having narrow cross-sectional area. Accordingly, the die cavity may not be completely filled with oxygen.

The present disclosure thus uses oxygen filling in a reverse direction, i.e. through the chill vent blocks on the upper end portions of the die. Therefore, oxygen may be first supplied to fill the die cavity, which is a core portion to control functional quality, and thereafter, to fill the gate, runner and sleeve. In this manner, oxygen filling required in the die cavity may be maximized efficiently, which is advantageous in forming the instantaneous vacuum in the cavity.

In the present disclosure, the oxygen supply may be made through the chill vent blocks 160 and 160-1 as described above. In addition, by the specification and structure of the chill vent blocks 160 and 160-1, it is possible to reduce the time for oxygen supply and to maximize the oxygen supply amount, effectively, and to prevent a leakage of the molten metal.

FIGS. 3A and 3B illustrate chill vent blocks, which are portions of a die for a vacuum die casting according to the present disclosure. FIG. 4 illustrates a portion of FIG. 3A.

The chill vent blocks may be formed in a pair to correspond to the fixed die 110 and the movable die 120, respectively. FIG. 3A illustrates the chill vent block 160 formed on the fixed die and FIG. 3B illustrates the chill vent block 160-1 formed on the movable die. The chill vent blocks may be coupled to each other to form a chill vent flow path. The chill vent blocks 160 and 160-1 may correspond to each other in a male and female relationship. The male and female relationship may be opposite to that depicted and described in the disclosed embodiments.

For example, the chill vent block 160 on the fixed die 110 may have: a molten metal inlet 161 communicating with an upper end of the cavity and introducing the molten metal; a molten metal solidification flow path 162 extending from the molten metal inlet 161 in a width direction; and a gas discharge hole 163 formed above the molten metal solidification flow path 162 and allowing the gas discharge hole 163 to communicate with the vacuum decompression line 220.

The chill vent block 160-1 on the movable die 120 may also have a molten metal solidification flow path 162-1 corresponding to the molten metal solidification flow path 162 of the chill vent block 160 on the fixed die 110. The two molten metal solidification flow paths 162 and 162-1 may be coupled to each other to form a flow path therebetween.

In addition, a gas discharge hole 163-1 may be formed above the molten metal solidification flow path 162-1. As illustrated in the drawing, a gas discharge hole 163-1 of the chill vent block 160-1 on the movable die 120 may be closely inserted into the corresponding gas discharge hole 163 of the chill vent block 160 on the fixed die 110. The insertion structure may also be provided or formed in the reverse or vice versa.

In general die casting of the prior art, the chilled vent is designed to have a maximum gap of 0.3 to 0.5 mm to prevent the leakage of the molten metal, which is injected at high speed and high pressure. However, in the present disclosure, in order for efficient vacuum compression and oxygen supply, the molten metal inlet 161 and the molten metal solidification flow path, which is formed by the two molten metal solidification flow paths 162 and 162-1, may have gaps different from each other.

In other words, the molten metal inlet 161 may have a gap g0 of 3 to 4 mm. The molten metal solidification flow path may be designed to have a gap g1 or g2 of 1.0 to 1.2 mm, which is 3 to 4 times greater than the prior known gap. The same gap may be maintained from g1 to g2. In this manner, the active oxygen may be smoothly supplied and the supply time may also be minimized.

Further, the gap of the molten metal inlet 161 may be gradually reduced to the gap of a point (indicated as g1) where the molten metal solidification flow path starts.

To this end, the chill vent blocks 160 and 160-1 may have a different shape from the general or conventional chill vent. In other words, in order for smooth vacuum compression and oxygen supply while preventing leakage of the molten metal when the injection is processed at high speed and high pressure, the chill vent blocks 160 and 160-1 may be characteristically designed to have a shape like a washboard to maximize a cross-sectional area of the molten metal solidification flow path and to have a conformal cooling channel in which a coolant is allowed to efficiently flow. The conformal cooling channel having a curved form is more efficient.

In other words, as illustrated in the drawings, a cross section of the molten metal solidification flow path may have triangular, i.e., saw tooth like, uneven structures. In such a manner, alternating convex portions 162-3 and concave portions 162-4 are repeated and bent several times in each of the molten metal solidification flow paths 162 and 162-1. In an example, the convex portions 162-3 may be formed at least six (6) times and at most fifteen (15) times.

The convex and concave portions formed in a continuously bent or saw tooth shape may be advantageous to prevent leakage of the molten metal when having more stages. On the other hand, the convex and concave portions having less stages may reduce losses, such as in a recovery rate and a die size. Therefore, in order to prevent both leakage of the molten metal and losses, the convex and concave portions need to have the above numbers of the stages.

In addition, the interior angle of each of the convex portions 162-3 and the concave portions 162-4 may have an angle of 40 degrees or less, as in an example of FIG. 5B, rather than about 90 degrees, as illustrated in FIG. 5A.

When the interior angle is about 90 degrees, as illustrated in FIG. 5A, the molten metal may be easily discharged. However, when the interior angle is 40 degrees or less, as illustrated in FIG. 5B, cross-sectional areas of the molten metal solidification flow path may be advantageously maximized. As a result, during passing over the convex portions 162-3, each having a narrow cross-sectional area, the molten metal may be more easily solidified and leakage of the molten metal may thus be prevented.

As described above, in the present disclosure, defects caused in die casting may be minimized without any high vacuum die casting equipment and physical properties of the cast product may thus be improved. The following table shows the above comparison.

TABLE 1 Physical Gas content property Type (100 g of Al) (MPa) Equipment price General die casting  20 cc 180~200 — High vacuum die  1 cc 260~280 about 120 million casting (Korean won) Die casting in present 1~3 cc 240~260 about 20 million disclosure (Korean won)

Although the present disclosure has been described with reference to the accompanying drawings, it should be apparent to those having ordinary skill in the art that the present disclosure is not limited to the embodiments described above. The disclosed embodiments may be variously modified and altered without departing from the spirit and scope of the present disclosure. Therefore, these modifications and alterations are to be considered to belong to the claims of the present disclosure, and the scope of the present disclosure is to be interpreted on the basis of the following claims. 

What is claimed is:
 1. A vacuum die casting method, comprising: coupling a fixed die and a movable die to each other; closing a molten metal pouring hole, which is formed in a sleeve, using an injection plunger operated in the sleeve, which is formed on a lower side of the fixed die or the movable die; performing vacuum decompression in a cavity formed between the fixed die and the movable die using a vacuum decompression device connected to chill vent blocks, which are provided on upper portions of the fixed die and the movable die; supplying oxygen in the cavity using an oxygen supply device connected to the chill vent blocks after completing the performing of the vacuum decompression; and supplying a molten metal to the cavity through the molten metal pouring hole.
 2. The vacuum die casting method of claim 1, wherein the vacuum decompression device is connected to the chill vent blocks through a vacuum decompression line, and wherein the oxygen supply device is connected to the chill vent blocks through the vacuum decompression line and an oxygen supply line.
 3. The vacuum die casting method of claim 1, wherein, in the performing of the vacuum decompression, a vacuum decompression valve, which is provided on the vacuum decompression line, is controlled to be opened following a signal indicating the molten metal pouring hole is closed.
 4. The vacuum die casting method of claim 3, wherein the performing of the vacuum decompression is performed until a pressure in the cavity reaches 200 mmHg or less.
 5. The vacuum die casting method of claim 1, wherein the supplying of the oxygen in the cavity includes performing a primary oxygen supply until the pressure in the cavity reaches 1200 mbar or more; the supplying of the molten metal to the cavity is performed after the primary oxygen supply is completed; and the supplying of the oxygen in the cavity further includes performing a secondary oxygen supply to supply less oxygen than the primary oxygen supply after the supplying of the molten metal to the cavity is started.
 6. The vacuum die casting method of claim 5, wherein the molten metal is molten aluminum.
 7. The vacuum die casting method of claim 5 further comprising: proceeding with an injection by operating the injection plunger after the supplying of the molten metal to the cavity; and completing the secondary oxygen supply at a time point when the injection plunger passes the molten metal pouring hole during the injection.
 8. A die for a vacuum die casting, the die comprising: a fixed die and a movable die; an injection plunger operated in a sleeve, which is formed on a lower side of the fixed die or the movable die; a vacuum decompression device connected to chill vent blocks, which are provided on upper portions of the fixed die and the movable die, and configured to perform vacuum decompression in a cavity formed between the fixed die and the movable die; and an oxygen supply device connected to the chill vent blocks and configured to supply oxygen in the cavity.
 9. The die of claim 8 further comprising: a vacuum decompression line connected from the vacuum decompression device to the chill vent blocks; a vacuum decompression valve provided on the vacuum decompression line; an oxygen supply line connected from the oxygen supply device to the chill vent blocks; and an oxygen supply valve provided on the oxygen supply line.
 10. The die of claim 9, wherein the vacuum decompression valve is controlled following a signal of a vacuum sensor provided in the cavity; and wherein the oxygen supply valve is controlled following a signal of an oxygen sensor provided in the cavity.
 11. The die of claim 8, wherein the chill vent blocks are formed as a pair in the fixed die and the movable die, respectively, and wherein the chill vent blocks have a molten metal inlet communicating with an upper end of the cavity and introducing the molten metal when the fixed die and the movable die are coupled to each other, and have a molten metal solidification flow path extending from the molten metal inlet and a gas discharge hole communicating with the vacuum decompression line.
 12. The die of claim 11, wherein the molten metal solidification flow path has a gap of 1.0 to 1.2 mm.
 13. The die of claim 11, wherein a cross section of the molten metal solidification flow path has triangular uneven structures such that alternating convex portions and concave portions are repeated and bent several times.
 14. The die of claim 13, wherein an interior angle of each of the convex portions and the concave portions is 40 degrees or less.
 15. The die of claim 8, wherein the chill vent blocks have a conformal cooling channel in which a coolant is allowed to efficiently flow. 